If the status of your SMS is "Delivered", but your recipient says he did not receive the message, there are a few things you can check:
It could be that the sender was added to his/her "blocked numbers list". To check this on the device:
* Iphone: Settings => Phone => Call Blocking & Identification. Or click here for more detailed info.
* Android: Messages => Parameters => blocked numbers. (It can vary depending of the application that was used.) Or click here for more detailed info.
If he/she finds the number under that list, please ask to remove it and request a new SMS.
If this doesn't help to solve the issue, please ask your recipient to check directly with his/her operator customer support, as they won't offer us support for single user complaints where we received positive DLR.